The present invention relates to the hardening of ferrous or iron based powdered metal part. It is known to harden a ferrous part by gas nitrocarburizing of the part. This process accomplishes hardening by the formation of an epsilon iron nitride compound of relatively low temperatures which is desirable as less part distortion is produced, limiting the needed amount of subsequent machining that may be necessary for the part's ultimate use.
Such hardened parts are particularly desirable in applications where the part is required to bear against another part and must be able to withstand the wear induced by the resulting contact. Automotive parts are one example of the area of use where such hardened parts are particularly desired because of the many instances where one part must interract with another part.
While the surface hardening of the powdered metal part is desirable, it is equally important that the part retain its inner or core ductility after the hardening. Thus, the formation of epsilon iron nitride beneath the surface of the part by penetration of the nitrocarburizing gases through the interconnected pores causes the same hardening effect deep into the part, producing an unwanted brittleness of the part. As is commonly the case, such parts are initially fabricated by sintering which achieves a part that permits easy penetration of the hardening environment through the inherent porosity of sintered powdered metal parts.